TW202210929A - Reflective slm image projector with intermediate image plane - Google Patents

Abstract

An image projector includes a spatial light modulator (SLM) illuminated by light from an illumination source so as to reflect light corresponding to an image. A first optical arrangement with positive optical power focuses light reflected from the SLM at an image plane. A second optical arrangement with positive optical power collimates light from the image plane as a collimated output image.

Description

Reflective SLM image projector with intermediate image plane

The present invention relates to image projectors, and in particular to image projectors based on reflective Spatial Light Modulators (SLMs).

Many display systems, especially near-eye displays, employ an image projector that outputs a collimated image into a Light-guide Optical Element (LOE) that transmits the image In front of the user's eye, the image is coupled out for viewing in front of the user's eye.

Image projectors typically include image generating elements and collimating optics to generate a collimated image output. One desirable option for image generators is a reflective spatial light modulator (SLM), typically implemented as a Liquid-Crystal On Silicon (LCOS) wafer, that utilizes polarized illumination to Illuminates and reflects illumination with selectively rotated polarizations corresponding to image pixel intensities. The images were then selected by a Polarizing Beam Splitter (PBS) before reaching the collimating optics.

The present invention is an image projector based on a reflective SLM and having an intermediate image plane.

In accordance with the teachings of embodiments of the present invention, there is provided an image projector for outputting a collimated image, the image projector comprising: (a) an illumination source; (b) a spatial light modulator provided by the illumination source from (c) a first optical device having positive optical power arranged to focus the light reflected from the spatial light modulator at the image plane; and (d) having positive light A second optical device of power arranged to collimate light from the image plane into a collimated output image.

According to another feature of embodiments of the present invention, at least the second optical device includes a reflective lens associated with the surface of the ion containing the polarizing beam splitter.

According to another feature of the embodiments of the present invention, the fluorine and the light guide optical element (LOE) Optically integrated, the light guide optical element has a pair of parallel major outer surfaces for guiding light by internal reflection, wherein the portion of the ion between the polarizing beam splitter and the LOE has an outer surface that is in contact with the LOE's One of the major outer surfaces is coplanar and forms an extension of the one of the major outer surfaces of the LOE.

According to another feature of embodiments of the invention, the light path from the spatial light modulator via the first optical device and the second optical device to the image output passes through two polarizing beam splitters, and wherein the image planes are located at two between polarizing beam splitters.

According to another feature of embodiments of the invention, the two polarizing beam splitters are parallel.

According to another feature of embodiments of the present invention, two polarizing beam splitters are included within the lens, and wherein the first optical device and the second optical device are implemented as reflective lenses associated with the surface of the lens.

According to another feature of embodiments of the invention, there is also provided at least one optical element spatially associated with the image plane.

According to another feature of embodiments of the invention, the at least one optical element comprises a field lens.

According to another feature of embodiments of the invention, the at least one optical element includes a diffuser.

According to another feature of embodiments of the invention, the at least one optical element comprises a microlens array.

204: Light guide optics

316: Lighting source

318: Polarizing Beam Splitter

320: Spatial Light Modulator (SLM)

322: First Optical Device

322': First Optical Device

324: Image plane

326: Polarizing Beam Splitter

328: Second Optical Device

330: 馜鏡

332: outer surface

334: Aperture

336: samsara

338: Buffer Layer

424: Optical Components

LCOS: Liquid Crystal on Silicon

The invention is described herein, by way of example only, with reference to the drawings, in which:

1A is a schematic side view of an image projector constructed and operated in accordance with the teachings of embodiments of the present invention;

FIG. 1B is a view similar to FIG. 1A showing a variant implementation of an image projector including optical elements at the image plane of the projector; and

2 is a schematic side view of an image projector constructed and operative in accordance with the teachings of another embodiment of the present invention.

The present invention is an image projector for outputting collimated images.

The principles and operation of the image projector according to the present invention may be better understood with reference to the drawings and accompanying description.

Referring now to the drawings, FIG. 1A illustrates a non-limiting implementation of an image projector for outputting collimated images constructed and operative in accordance with the teachings of embodiments of the present invention. In general, an image projector includes a spatial light modulator (SLM) 320 that is illuminated by light (schematically represented by arrows) from an illumination source 316 to reflect light corresponding to the image. A first optical device 322 having a positive optical power is arranged to focus light reflected from the SLM 320 at the image plane 324 . A second optical device 328 having a positive optical power is arranged to collimate light from the image plane 324 into a collimated output image.

The focusing of light from the reflective SLM at the intermediate image plane 324 within the image projector element provides significant advantages compared to arrangements in which the SLM itself must be at the focal plane of the collimating optics. Specifically, in order to achieve a large-angle Field Of View (FOV) of the projected image with a relatively small projector, the focal length of the collimating optics should be relatively short. However, reflective SLMs require a lighting system for front lighting of the SLM. This limits how close the SLM can be positioned to the collimation optics, often resulting in increased size of the collimation optics, reduced FOV, and/or other design compromises. By providing the first optics 322 to generate an image at the image plane 324 within the projector, these design constraints are lifted, leaving ample room for the illumination system while allowing the use of collimating optics with short focal lengths. This and other advantages of the present invention will become more apparent from the following description and drawings.

In some particularly preferred implementations, at least the second optical device 328 is implemented as a reflective lens associated with the surface of the lens 330 containing the polarizing beam splitter 326 . Advantageously, the image plane 324 may fall at a certain plane within the horizon 330 without any specific structure being present at that plane. Alternatively, in certain implementations, it may be desirable to arrange one or more optical elements at or near the focal plane, as will be exemplified below with reference to Figure IB.

In some applications, the image projector is integrated with a light guide optical element (LOE) 204, which is typically a slab-type waveguide with two parallel main outer surfaces within which Image illumination propagates through Total Internal Reflection (TIR). In certain preferred implementations, the portion of the lens 330 between the polarizing beam splitter 326 and the LOE 204 The minute has an outer surface 332 that is coplanar with, and forms an extension of, one of the major outer surfaces of the LOE 204 . This facilitates filling optical aperture 334 into LOE 204 by generating a reflected (conjugate) image at the LOE entrance. The LOE 204 may be any type of LOE known in the art, eg, a LOE that employs sets of partially reflective inner surfaces to achieve aperture expansion in one or two dimensions and couple out image illumination toward the viewer's eye. Alternatively, or in addition, the LOE may employ diffractive optical elements to achieve one- or two-dimensional optical aperture expansion and out-couple image illumination toward the viewer's eye, all of which are known in the art.

In the preferred but non-limiting example shown in FIG. 1A , the light path from SLM 320 to the image output via first optics 322 and second optics 328 passes through polarizing beam splitter 318 and polarizing beam splitter 326 The two polarizing beam splitters, and the image plane 324 is located between the two polarizing beam splitters. Advantageously, the two polarizing beam splitters, polarizing beam splitter 318 and polarizing beam splitter 326, are parallel. This helps to minimize noise in the output image, since any raw illumination (not fully filtered) from illumination source 316 that leaks through PBS 318, for example due to skewed angles of incidence, will The exact same conditions are encountered at PBS) 326, and will therefore also pass through PBS 326 without becoming mixed with the image illumination.

The image projector of the present invention provides considerable design freedom with respect to the position of the intermediate image plane, the power of the collimation optics and the overall size of the optics. If the intermediate image plane 324 is designed to be closer to the second optics 328, the size of the optics can be reduced and/or limited by optical aberrations and the desired size of the intermediate image compared to the SLM wafer size Increase FOV. The first optics 322 are then designed according to the desired location of the intermediate image and its dimensions relative to the size of the SLM wafer.

In the implementation shown here, two polarizing beamsplitters, polarizing beam splitter 318 and polarizing beam splitter 326, are included within ion 330, and the first optical device 322 and the second optical device 328 are two It is implemented as a reflective lens associated with the surface of the crystal. Each lens is integrated with a quarter-wave plate that achieves a rotation of the polarization after two passes generated by reflection to achieve transmission-followed-by reflection at the corresponding PBS surface -reflection) or reflection-followed-by-transmission, as known in the art.

Illumination source 316 may be any suitable illumination source known in the art, including but not limited to LEDs and laser diodes. Illumination sources can include sources of different colors that can be quickly Fast switching to illuminate the color separation image within a single frame period of the video to generate a color image. The illumination source may include various optical components for directing and/or homogenizing illumination, all of which are known in the art.

SLM 320 may be any suitable type of SLM, and in particular is a front emitting SLM. A particularly preferred example of an SLM suitable for implementing the present invention is an LCOS (liquid crystal on silicon) wafer. The SLM is typically a rectangular array that also extends into the page in the side view shown here, and all other optical components shown here similarly extend into the page according to the relative size defined by the aspect ratio of the SLM, which is important for It will be apparent to those of ordinary skill in the art.

It should be noted that the light path shown here is for the light of the central pixel of SLM 320 illuminated by light from illumination source 316 reflected from PBS 318 . Divergent light reflected from the SLM passes through PBS 318 and is focused by first optics 322 . The converged light is again reflected by PBS 318 to generate an image at image plane 324 . Divergent light from this plane is reflected by PBS 326 onto second optics 328 . The reflected collimated light is coupled into the waveguide while some of the reflected collimated light is reflected by the outer surface 332 .

FIG. 1B shows an image projector that is generally equivalent to the image projector of FIG. 1A , but in this image projector at or near image plane 324 (ie, spatially different from that of FIG. 1B ). Associated with the image plane 324) at least one optical element 424 is arranged. Optical element 424 may be a lens (typically a Fresnel lens) arranged to at least partially correct the field curvature of the optical device. Additionally or alternatively, optical element 424 may include a diffuser or Micro-Lens array (MLA) for adjusting the spread of illumination to output across the image projector The optical aperture produces a more uniform output intensity. In all other respects, the image projector of FIG. 1B is structurally and functionally equivalent to the image projector of FIG. 1A described above.

Turning now to Figure 2, there is shown a second implementation of the present invention that is functionally similar to the implementation of Figure 1 but employs free space optics to generate an internal image plane.

Specifically, in this case, the SLM 320 illuminated by the illumination source 316 via the PBS 318 is aligned with the first optical device 322 ' , here implemented to typically employ one or more refractions Free space optics of the lens arranged to focus light reflected from the SLM 320 at the image plane 324 . A second optical device 328 having a positive optical power is arranged to collimate light from the image plane 324 into a collimated output image (shown here entering the LOE 204 at the entrance aperture 334). Here, the second optics 328 is implemented as a reflective lens associated with the surface of the PBS 330 including the PBS 326 to direct light from the image plane 324 towards the collimating optics. The reflected collimated light (after passing through the quarter wave plate twice as mentioned above) passes through PBS 326 to reach aperture 334 - partly directly to aperture 334 and partly after additional reflection at outer surface 332 Aperture 334 is reached.

An in-coupling junction 336 is provided to facilitate in-coupling of image illumination after the first optical device 322 ' . An air space or buffer layer 338 of low refractive index material is provided to maintain TIR conditions for the collimated light propagating from the second optical device 328 to the exit/entry aperture 334 .

It should be understood that the above description is intended to serve as an example only and that many other embodiments are possible within the scope of the invention as defined by the appended claims.

204: Light guide optics

316: Lighting source

318: Polarizing Beam Splitter

320: Spatial Light Modulator (SLM)

322: First Optical Device

324: Image plane

326: Polarizing Beam Splitter

328: Second Optical Device

330: 馜鏡

332: outer surface

334: Aperture

Claims (10)

An image projector for outputting a collimated image, the image projector comprising: (a) a source of illumination; (b) a spatial light modulator illuminated by light from the illumination source to reflect light corresponding to an image; (c) a first optical device having a positive optical power, arranged to focus light reflected from the spatial light modulator at the image plane; and (d) A second optical device having a positive optical power, arranged to collimate light from the image plane into a collimated output image. The image projector of claim 1, wherein at least the second optical device includes a reflective lens associated with the surface of the ion containing the polarizing beam splitter. The image projector of claim 2, wherein the ceiling is optically integrated with a light guide optical element (LOE) having a pair of parallel major outer surfaces for guiding light by internal reflection, Wherein, the portion of the crystal between the polarizing beam splitter and the light guide optical element has an outer surface, the outer surface and one of the main outer surfaces of the light guide optical element are coplanar and form an extension of the one of the major outer surfaces of the light guide optical element. The image projector of claim 1, wherein the light path from the spatial light modulator to the image output via the first optical device and the second optical device passes through two polarizing beam splitters , and wherein the image plane is located between the two polarizing beam splitters. The image projector of claim 4, wherein the two polarizing beam splitters are parallel. 4. The image projector of claim 4, wherein the two polarizing beam splitters are included in a lens, and wherein the first optical device and the second optical device are implemented with the A reflective lens is associated with the surface of the crystal. The image projector of claim 1, further comprising at least one optical element spatially associated with the image plane. The image projector of claim 7, wherein the at least one optical element The piece includes a field lens. The image projector of claim 7, wherein the at least one optical element comprises a diffuser. The image projector of claim 7, wherein the at least one optical element comprises a microlens array.

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